This application is related to Japanese Patent Applications Nos. 2000-016672 filed on Jan. 26, 2000, 2000-156733 filed on May 26, 2000 and 2000-268870 filed on Sep. 5, 2000 whose priorities are claimed under 35 USC xc2xa7119, the disclosure of which is incorporated by reference in its entirety.
1. Field of the Invention
The present invention relates to a dye-sensitized solar cell utilizing a solid polyelectrolyte. More particularly, it relates to a dye-sensitized solar cell utilizing a crosslinked polymer compound obtained by polymerizing units having a specific structure.
2. Description of Related Art
When a photovoltaic material is irradiated with light, electrons restricted to an atom in the photovoltaic material are released by light energy to move freely, which generates free electrons and holes. The free electrons and the holes are efficiently separated so that electric energy is continuously extracted. That is, the photovoltaic material is capable of converting light energy to electric energy. Such photovoltaic material has been utilized as a solar cell and the like.
A dye-sensitized solar cell (hereinafter merely referred to as xe2x80x9csolar cellxe2x80x9d) has widely drawn attention because of its higher photovoltaic efficiency than other organic solar cells. The solar cell is comprised of an electrolyte solution layer sandwiched between a semiconductor electrode and a counter electrode. When the semiconductor electrode is irradiated with light, electrons are excited therein and transferred to the counter electrode through an electric circuit. The transferred electrons are re-transferred as ions to the semiconductor electrode through the electrolyte. This cycle is repeated to extract electric energy.
In a surface of the semiconductor electrode used as a photovoltaic material in the solar cell, a photosensitivity enhancing dye having an absorption spectrum in the range of visible rays is adsorbed. With respect to such solar cell, Japanese Patent No. 2664194 describes a solar cell utilizing a metal oxide semiconductor which adsorbs in its surface a photosensitivity enhancing dye comprising a transition metal complex. Published Examined Patent Application No. Hei 8 (1996)-15097 describes a solar cell utilizing a titanium oxide semiconductor doped with metal ions on which a layer of a photosensitivity enhancing dye comprising a transition metal complex or the like is formed. Further, Published Unexamined Patent Publication-No. Hei 7 (1995)-249790 discloses a solar cell utilizing a semiconductor for photovoltaic conversion obtained by heating a solution of a photosensitivity enhancing agent in ethanol to reflux on a surface of the semiconductor.
FIG. 5 is a schematic sectional view of a major part illustrating a layered structure of a prior art solar cell utilizing an oxidation-reduction electrolyte solution. The solar cell is manufactured in the following steps. therein. A counter electrode 55 coated with a catalyst such as platinum 56 or the like is
First, one a transparent conductor 52 formed on a surface of a transparent support 51, a semiconductor layer 53 of titanium oxide or the like is formed and a dye is absorbed coupled with the transparent support 51 so that the semiconductor layer 53 and the platinum 56 are faced to each other, and then an electrolyte solution 54 is injected therebetween. Thereafter, the circumference of the coupled structure is sealed with an epoxy resin 57, 58 or the like.
In order to avoid solution leakage of the electrolyte solution layer 58, Japanese Unexamined Patent Publications Nos. Hei 8 (1996)-236165 and Hei 9 (1997)-27352 describe a solar cell in which the electrolyte solution layer is solidified. A known method of solidifying the electrolyte solution layer is as follows. First, iodide (lithium iodide or the like) which functions as an oxidation-reduction seed is dissolved in a solution obtained by dissolving a monomer represented by the general formula (IV): 
wherein R5 and R6, equal to or different to each other, are a hydrogen atom or a methyl group, R7 is a hydrogen atom or a lower alkyl group, x is an integer of 1 or more, y is an integer of 0 or more and y/x is 0 to 5 in ethylene glycol and the solution is impregnated into the porous semiconductor layer. Then, it is polymerized by ultraviolet rays or heat to obtain a polymer compound and iodine which functions as another oxidation-reduction seed is doped by sublimation. Thus, the solidified electrolyte layer is formed.
However, it is difficult to obtain a crosslinked polymer compound by the above-mentioned polymerization since the monomer of the general formula (IV) has only one vinyl group. The polymerization only with the monomer of the general formula (IV) generates a linear or a branched polymer compound which is not crosslinked, so that retention of the electrolyte and the electrolyte solution is reduced and mechanical strength becomes poor. Further, it is also difficult to control the amount of iodine doped in the polymer compound by the above-described sublimation, so that it is not preferable in view of reproducibility.
In view of the above drawbacks, the present invention has been achieved to provide, with use of the crosslinked polymer compound, a dye-sensitized solar cell including a polyelectrolyte having excellent retention of the solution and favorable mechanical strength. The invention also provides a method of manufacturing the dye-sensitized solar cell in which the polyelectrolyte is produced with good precision by impregnating a solution of two kinds of electrolytes which act as oxidation-reduction seeds in the crosslinked polymer compound.
The inventors of the present invention has eagerly studied to solve the above drawbacks and found that the crosslinked polymer compound obtained by polymerizing specific monomers exhibits great retention of solution and mechanical strength. Thus, the present invention has been completed.
According to the present invention, provided is a dye-sensitized solar cell comprising a porous semiconductor layer in which a dye is adsorbed and an electrolyte which are sandwiched between a transparent conductive film formed on a surface of a transparent substrate and a conductive substrate, wherein the electrolyte is retained in a crosslinked polymer compound.
Still according to the present invention, provided is a method of manufacturing a dye-sensitized solar cell comprising the steps of:
(a) forming a transparent conductive film on a surface of a transparent substrate;
(b) forming a porous semiconductor layer on a surface of the transparent conductive film;
(c) impregnating a dye solution in the porous semiconductor layer;
(d) impregnating a solution containing units capable of forming a crosslinked polymer compound through polymerization in the porous semiconductor layer to form a polymer compound on the surface and in the inside of the porous semiconductor layer;
(e) impregnating an electrolyte solution in the polymer compound to form an electrolyte; and
(f) placing a conductive substrate and sealing a circumference portion thereof.
These and other objects of the present application will become more readily apparent from the detailed description given hereinafter. However, it should be understood that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description.